X4 Step size

Discussion in 'X4M03' started by Nikolay Kovachev, Oct 10, 2018.

  1. Nikolay Kovachev

    Nikolay Kovachev New Member

    Hi,
    how can I decrease the step size? I'm interested in inspection of small objects 20cmX20cm on 1/2 meters from the radar. The current step size is ~9.88/1536 and I wonder what is the best way to achieve something like 2/1536.

    Thanks
     
  2. NSANGOU CHOUAIBOU

    NSANGOU CHOUAIBOU Active Member

    Hi Nikolay,

    For X4 SoC, each radar bin is 5.14 cm and you have 188 baseband complex bins and 1536 RF bins. Please take a look at this thread : https://www.xethru.com/community/threads/whats-is-the-meaning-of-rf-data.370/#post-1722

    For sensors default parameters, you can find all information in their respective datasheet :

    - Step size between possible range settings is 5.14 cm.

    - Minimum start of detection zone is 0.40 m for both X4M300 and X4M200 sensors

    - Maximum end of detection zone is 9.40 m for X4M300 presence sensor and 5.00 m for X4M200 respiration sensor.

    - Minimum size of detection zone is 0.20 m for both X4M300 and X4M200 sensors

    - Maximum size of detection zone is 9.00 m for X4M300 presence sensor and 4.60 m for X4M200 respiration sensor.

    For all Xethru module, you can set a zero meter reference (frame offset setting)

    Best regards,
    Chouaibou.
     
    Last edited: Oct 10, 2018
    Charlie Shao likes this.
  3. Nikolay Kovachev

    Nikolay Kovachev New Member

    Hi,
    thanks Chouaibou.
    That's the standard configuration. I have X4M03 I'm looking for a way to tune it and reduce the RF bins step maximally. One of my suggestions is to tweak the receiver timing, but there is a note that this is not recommended in the datasheet. What would happen if I increase the clock of the samples? Am I risking to burn the chip or just risking to loose the accuracy of some pre build algorithms?

    Currently the RF step is ~0.65cm, but I would like to achieve 0.01cm.
     
  4. NSANGOU CHOUAIBOU

    NSANGOU CHOUAIBOU Active Member

    Hi Nikolay,
    The system sampling frequency is fixed and you can't change it ! Interpolation can help to calculate in between bins less than ~0.65cm, but high SNR is very important to get high accuracy.
    For small variations around any distance in the radar setting range, you can use phase information for very high accuracy distance relative variation, thanks to Xethru performance, but absolute distance calculation is impossible due to the -pi, +pi phase wrap.

    Best regards,
    Chouaibou.
     
    Charlie Shao likes this.
  5. Nikolay Kovachev

    Nikolay Kovachev New Member

    Hi,
    can I use the rx pll div and post div to increase the receiver frequency at least slightly?
     
  6. NSANGOU CHOUAIBOU

    NSANGOU CHOUAIBOU Active Member

    Hi Nikolay,
    UWB impulse radar sends pulses and sample the echos after a delay according to the range setting. There is a very accurate timing in the chip between TX and RX.

    Best regards,
    Chouaibou.
     
  7. Nikolay Kovachev

    Nikolay Kovachev New Member

    Hi,
    if I understood the data sheets and the user guides correctly the range settings do not change the step size. My tests seems to support that as well. If we tune the RX dividers we should be able to reduced the step size, sampling the physical samplers more often. Of course the range will decrease as we have 1536 bins only. I'm interested in objects up to 2 meters away and this is not a problem. What worries me is the note in the X4 datasheet:
    "
    The receiver is designed to operate with a maximum clock frequency of 1944 MHz. It is not recommended to use the receiver with non-default feedback divider settings.
    "
    If I change the RX dividers this will affect the RX frequency and my question is what is the risk of doing that?

    Currently the R&D goes well and decreasing the step size is important to achieve our goals. Will appreciate help with that.

    Regards,
    Kovachev
     
  8. NSANGOU CHOUAIBOU

    NSANGOU CHOUAIBOU Active Member

    Hi Nikolay,
    It is difficult to answer to your question as you intend to use non recommanded feedback divider settings. May be you can perform some experiments but it's your responsability.
    The step size is important to achieve your goals, but are you pretty sure that the best method is to modify the Rx dividers ?

    Best regards,
    Chouaibou.
     
  9. Nikolay Kovachev

    Nikolay Kovachev New Member

    Hi,
    That's why I'm asking this question :) I'm looking for the best way and I hoped someone with enough internal knowledge will get back to me. Indeed the risk is on me, what I want to know is do I need to look for cooling and what might get affected from the change.

    Regards
     
  10. NSANGOU CHOUAIBOU

    NSANGOU CHOUAIBOU Active Member

    Hi Nikolay,
    Sorry for my answer. I wish you all the best in the implementation of your project.

    Best regards,
    Chouaibou.
     
  11. Nikolay Kovachev

    Nikolay Kovachev New Member

    Hi Chouaibou,
    any suggestions are mostly appreciated. Thanks.